Heart valve sewing prostheses are suturable prosthetic devices that can be implanted in hearts to support or replace the function of the native heart valve. One heart valve sewing prosthesis is an annuloplasty ring. An annuloplasty ring is a ring or annular shaped device including a round outer surface having an outer diameter approximating the desired inner diameter of the tissue near the valve where the ring is to be implanted. The ring generally has an inner stiffening member, which can be formed of silicone. The ring outer surface can be formed of a fabric, such as knitted or braided polyester, for example Dacron®. The annuloplasty ring can be inserted into place and sewn to the surrounding valve annulus tissue using sutures passing through the fabric and through the tissue.
Another heart valve sewing prosthesis is an annuloplasty band. An annuloplasty band is similar in some respects to an annuloplasty ring. The annuloplasty band can have an arcuate or circular shape, and an open circumferential gap along one side, rather than being closed upon itself as is an annuloplasty ring. The annuloplasty band can be formed of an inner stiffening member surrounded by fabric. The outer fabric can receive sutures through the fabric, securing it to the surrounding tissue.
Annuloplasty rings and bands can be used in conjunction with valvular reconstructive surgery, to correct heart valve defects such as stenosis or valvular insufficiency. Many such defects are associated with dilation of the valve annulus. Such dilation can prevent competence of the valve and can cause distortion of the normal shape of the valve orifice. Annuloplasty rings generally entirely encompass the anterior and posterior portions of the valve annulus, while the annuloplasty bands generally encompass only a portion of the valve annulus.
Other heart valve prostheses include prosthetic heart valves, such as mechanical prosthetic heart valves and bioprosthetic heart valves. Mechanical heart valves can include a metal housing containing a metal valve plate that open and closes about a pivot. The bioprosthetic heart valve can be made from porcine heart valves that have been fixed to reduce adverse reactions upon implant. The tissue or housing can be secured to the surrounding tissue using another heart valve prosthetic device, a sewing ring or cuff. The sewing ring or cuff generally includes a ring or cuff having an outer fabric layer. The sewing ring or cuff can come secured to the heart valve outer housing. The sewing ring acts as an intermediate body placed between the heart valve outer housing and the native heart tissue. The heart valve housing can be secured to the native tissue by passing sutures through the sewing ring or cuff and the surrounding tissue.
Materials used to fabricate heart valve sewing prostheses typically include polyester fabric. Invariably, the host responds to this material as a “foreign body” and this reaction complicates the healing process. An ideal prosthetic valve device should heal well without excessive tissue overgrowth, and allow for the establishment of a smooth neointima. By reducing the inflammatory response to the foreign material, it may be possible to resolve the post-implant inflammatory response at the acute phase, with concomitant optimal healing without the long-term scar formation and consequences of stenosis and regurgitation.
The use of non-biologic materials in prosthetic heart valves, such as sewing rings and stents in tissue valves are necessary to support the tissue components and facilitate attachment of valves to the native tissue. The implantation of these non-resorbable materials permanently changes the microenvironment of the valve tissue, and possibly the global environment of the cardiac system. Peri-operative implant protocols may require the removal of the native valve leaflet, and cutting away damaged and/or mineralized tissue. These operations cause a major trauma to the tissue. The tissue response to this traumatic injury involves inflammatory response to the initial wound bed created for the prosthetic valve, and to the implanted non-native material. The inflammatory response may be divided into the acute and chronic phases. Unresolved acute inflammatory response leads to a chronic phase response with potential fibrotic tissue formation.
Along with the chronic fibrotic scar formation, inflammatory cells and the accumulation of cellular and proteinaceous blood elements are deposited. The layer of deposited cells and other elements is often referred to a pannus. The pannus grows as an extension of the tissue healing around the sewing ring or other heart valve sewing prosthesis. As a result of the unresolved inflammatory response, the pannus can continue to grow, extending onto the leaflets causing progressive stenosis, occlusion of the valve orifice or stiffening of the cusps. It has been shown that pannus can creep onto the biologic part of the valve and causes stenosis and/or incompetence. Tissue overgrowth has also been shown to cause leaflet retraction in valves, leading to clinically significant regurgitation. Tissue overgrowth onto mechanical valves can obstruct the occluder causing failure of the valve. Pannus overgrowth on both tissue and mechanical valves may necessitate their removal. As a result of the exuberant pannus growth onto the sewing ring of the valves, removal becomes difficult, making subsequent operations even more challenging.
There is therefore the need for superior biomaterials that will promote post-implant wound healing with limited scar formation. In particular, there is a need for heart valve sewing rings, annuloplasty rings, and annuloplasty bands having improved biocompatibility characteristics.